ABSTRACT: Significance: An epidemic proportion of Americans (approximately 75-100 million) suffer from obesity and nonalcoholic fatty liver disease, a spectrum of progressive liver disease that include steatosis, non- alcoholic steatohepatitis (NASH), fibrosis and, eventually, cirrhosis, and hepatocellular carcinoma (HCC). There is no standard of care pharmacotherapy for NASH. Therefore, new therapeutic approaches are urgently needed. IL-17 is a critical mediator of liver fibrosis of different etiologies including NASH. We have recently demonstrated that blocking of IL-17 signaling in IL-17RA-/- mice attenuated development of cholestatic and toxic liver fibrosis by 75%, suggesting that IL-17 may serve as a novel target for anti-NASH therapy. Expression of IL-17 cytokine is regulated by the nuclear receptor retinoid-related orphan receptor ?t (ROR?t), which belongs to a ?druggable? class of proteins that are targeted by 15% of prescribed drugs. Hypothesis: We hypothesize that a new class of ROR? inverse agonists identified in our labs will most effectively attenuate the development of NASH (steatohepatitis and fibrosis) via inhibition of IL-17 signaling. Preliminary Data: Genetic deletion of IL-17 signaling attenuates NASH-induced liver fibrosis in two mouse models of NASH: the high fat diet induced-, and Mup-uPA genetic- models of NASH. On the drug discovery front, we identified 3 new classes of ROR? inverse agonists, which based on initial medicinal chemistry studies on one series, demonstrate structure activity relationships (SAR), potency against IL-17 in hPBMCs (IC50 = ~200nM), oral bioavailability (70%), and effective inhibition of cholestatic and toxic fibrosis in mice. Specific Aims: We will prove the concept that ROR? inverse agonist compounds are therapeutically efficacious in preclinical models of NASH thus justifying the effort to develop these as drugs for NASH patients (Phase II SBIR). Aim 1. We will use medicinal chemistry/structure based design to optimize ROR? potency, selectivity against other nuclear receptors, and in vitro absorption, distribution, metabolism, and excretion (ADME) properties of an ROR? inverse agonist series. Aim 2, we will test if ROR? inverse agonists from Aim 1 have anti-IL-17 activity in primary human Peripheral Blood Lymphocytes (PBLs), primary human Kupffer cells, Hepatic Stellate Cells and hepatocytes (identified as IL-17 target cells), and use pharmacokinetic studies to select compounds with an effective pharmacological exposure in mice. Aim 3. We will test if optimized ROR? inverse agonists are well tolerated in mice and are therapeutically effective in two preclinical models of NASH: the ?fast food diet? (FFD) and Mup-uPA transgenic mice. These studies will establish ROR? inverse agonists as a new therapy for NASH. Further, the patentable and drug-like leads produce herein could rapidly be translated to the clinic and developed as a targeted therapy for NASH patients.